The liquid can be placed inside the machine by right-clicking the machine with a bucket of this liquid in hand, by piping it inside or by placing it inside with golems. The machine has internal liquid buffer of 16000 mb.

"You've had so much success with essentia distillation that you've decided to expand upon the ways you can break things down. The alchemical boiler works in much the same manner as the alchemical furnace but with liquids rather than items.

Add (or remove) liquid using buckets or through automation (such as certain golems).

The same things that speed up the operation of an alchemical furnace will help a boiler as well (such as alumentum).